This invention relates to molding compositions based on a linear, high-molecular weight polyester to which is admixed at least one additional synthetic resin, present as an aqueous latex, at an elevated temperature, under elevated pressure, and under the effect of strong shear forces.
The state of the art has included for a long time the practice of altering and improving the properties of a thermoplastic polymer by intimate admixture of an additional polymer (German Patent No. 1,260,135). Thus, DOS No. 2,622,876 describes molding compositions based on a polyester combined with 1-40 parts of a copolymer. The mixture of the components is effected in a closed system. This type of admixing permits only the use of copolymers which are introduced into the mixing unit in the solid phase, as powders, granules or crumbs. This procedure is unsuitable for incorporating into the polyester copolymers having a softening point below room temperature.
Such copolymers are normally produced as aqueous latices. It has been known to incorporate latices directly into thermoplastics by admixing the latex with the molten termoplastic (Adv. Polym. Techn. 3:41 et seq. [1983]; U.S. Pat. No. 3,742,093). The thus used thermoplastics had been obtained by polymerization exclusively. Resins obtained by polycondensation have not been described.
It is known from European Patent No. 56,123 to incorporate water-containing graft copolymers into saturated polyesters. However, the water content is restricted to at most 50% by weight. Since latices most contain more than 50% by weight of water, these must be processed and/or dehydrated for use in its method. Processing of the latices involves precipitation of the polymer, as well as partial removal of the water with the aid of mechanical methods. The significant drawback of this known process resides in having to work up the latex, instead of using it directly, without a previous treatment.